A man's strict vegan diet may have caused him to go blind, doctors say.

The 33-year-old man had been on a strict diet for 13 years which involved cutting out meat, eggs, dairy products, fish and all other sources of animal protein.

Vitamin supplementation is essential in persons who adhere to a strict vegetarian diet

Dr Dan Milea

When he was seen by doctors at the Pitie-Salpatriere Hospital in Paris part of his optic disc had deteriorated and he had "very poor vision".

Blood tests showed he was deficient in key minerals and vitamins. Supplements failed to improve his vision as his condition was too far advanced.

The man did not smoke or drink alcohol and his medical history was normal. tests did not uncover any other reason for his blindness.

Dr Dan Milea at the hospital said in the New England Journal of Medicine that the man adopted the diet to improve his health.

Deficiencies

The man had deficiencies in vitamins A, B, C, D and E and in the minerals zinc and selenium.

You have to really try to eat a poor diet to have the vitamin deficiencies of this man

George Rodger, The Vegan Society

Dr Milea said deficiencies of vitamins B12 and B1 were responsible for vision problems and had been documented in prisoners in World War II and in a Cuban epidemic of optic neuropathy - a severely blinding disease resulting from loss of the arterial blood supply to the optic nerve.

He warned: "Vitamin supplementation is essential in persons who adhere to a strict vegetarian diet, especially because vitamin deficiencies may cause severe, irreversible optic neuropathy."

The Vegetarian Society in the UK said meat and dairy-free diets were not dangerous if people ate sensibly. Blindness resulting from vegan diets was not something the society was aware of.

A spokeswoman said: "The problem with the man in question was that his diet was not balanced at all. Most vegetarians will normally take in cheese, dairy products and eggs and most vegans supplement their diets with soya milk and other foods, so they are getting vitamins and minerals.

"The essence of the situation is that if you are not having a balanced diet you are going to have problems. You need to take in as many different food sources as possible."

People who are already vegan or vegetarian or are considering a meat-free diet can contact the society for advice.

George Rodger, Chair of the Vegan Society, said any unbalanced diet would cause health problems.

But he added: "Vegans can be more than adequately nourished without resorting to supplements, pills or potions.

"You have to really try to eat a poor diet to have the vitamin deficiencies of this man."